It is conventional practice, within the electric utility industry, to use energy conversion devices of various capital costs, various fuel and operating costs, which devices meet instantaneous demands from the aggregated customers. Such demand varies from hour to hour, day to day and seasonally. One proposal for attempting to solve the variable demand problem involves the employment of a gas turbine which is powered by fuel gas and compressed air from a reservoir. The reservoir is recharged periodically by a compressor driven by the motor or heat engine combination during off-load periods only. Such proposals are described in U.S. Letters Pat. Nos. 3,935,469 and 3,831,373, French Patent 1,209,726 and Canadian Patent 596,277. However, such proposals have not been acceptable to the utility industry, among other reasons, because of the electrical-electrical conversion losses inherent in compressing air from an electric system off-peak generation and the failure to conserve capital equipment. Additionally, efficient use of capital requires that expensive heat conversion apparatus operate above average customer demand and with lower than average operating costs, while inexpensive apparatus, utilizing high cost fuels, must operate below average customer demand.
The utility customer commonly varies his demands so as to average about 50%-60% of the available apparatus capability.
It is to the economic advantage of the individual utility and the nation to reduce capital costs, increase output of individual apparatus and use so far as possible local low cost fuels. Requirements of both operation and apparatus need to be met to satisfy these goals, requirements which have not been provided by conventional practice.